You are correct that you cannot swap while actively in combat, but if I kill a single target and see a pile of goobers running towards me (or vice versa) I'm hoping for a quick way to switch builds and weapons in the brief interval of being out of combat.

Will give the plugins a try for item swaps - looks like one of them could also be a better way of handling warden gambits than the postit note I currently have stuck to my screen.

You are correct that you cannot swap while actively in combat, but if I kill a single target and see a pile of goobers running towards me (or vice versa) I'm hoping for a quick way to switch builds and weapons in the brief interval of being out of combat.

Will give the plugins a try for item swaps - looks like one of them could also be a better way of handling warden gambits than the postit note I currently have stuck to my screen.

Regarding the Warden, there are Warden specific plugins like WardenEase that do exactly that.

As for the "in combat" part that is a very specific thing to say given the context of LOTRO, as it is an on/off state in the game. If you mean a break in fighting, that is not per definition "in combat" as per what it specifically means in the game.

Finally, I can confirm that there is no way to quickly switch builds. Fastest would be to memorize the keybind that opens build window to open that and click.
There are other ways to do it with external software but the level of automation would break ToS for botting for sure, so not going to go into that.